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From: rdm2@nvuxr.UUCP (R McBurnett)
Newsgroups: net.unix
Subject: Re: SIGIOT and SIGEMT - and floating point on a PDP11
Message-ID: <124@nvuxr.UUCP>
Date: Thu, 5-Sep-85 15:30:48 EDT
Article-I.D.: nvuxr.124
Posted: Thu Sep  5 15:30:48 1985
Date-Received: Fri, 6-Sep-85 05:33:03 EDT
References: <2757@sun.uucp>
Organization: Bell Communications Research, Red Bank, NJ
Lines: 12

The EMT instruction on a PDP-11 computer is an emulate trap instruction
intended to emulate a real hardware interrupt.  At a guess it's original
purpose was to let software types tryout new software before the hardware was
ready.  THEN someone had a good idea about how to use it ?intelligently? in
an operating system.. Both RSX11-M and RT11 used it extensively.

BTW the TRAP instruction works the same way as EMT but to a different vector,
and is useful for user programs that want to test hardware interrupts.

Roe McBurnett		{ihnp4!packard,topaz}!nvuxr!rdm2
Bell Communications Research, Red Bank NJ